1. Field of the Invention
This invention relates to an improved process for the formation of polyurethane-ureas in a suspension polymerization medium. More particularly, it relates to a one-shot process for the preparation of an essentially linear polyurethane-urea granular solid from a diisocyanate, polyol, water reactant mixture.
2. Description of the Prior Art
The preparation of polyurethane-urea polymers is well known. Bayer et al., in the article entitled "New Types of Highly Elastic Substances, Vulcollanes," Rubber Chem. & Technol., 23, 817-818 and 824 (1950), report the formation of these polymers by the chain extension of isocyanate-terminated polyester polyurethanes with water, also see Muller et al., Ibid. 26, 494 and 502 (1953). The products from these chain extension reactions are most often obtained as solutions in organic solvents, stable aqueous dispersions or more or less unitary solid masses. Various aqueous systems of these materials are disclosed in U.S. Pat. Nos. 2,968,575; 3,148,173; 3,213,049; 3,281,397; 3,294,724; and 3,437,624. In U.S. Pat. No. 2,702,797 a mass polymerization method for the preparation of polyurethane-urea materials is disclosed which differs significantly from those methods used by Bayer et al and Muller et al. In this patent, it is disclosed that prepolymers are not necessarily used, but that all possible reactants, i.e., the polyether glycol, polyisocyanate and water, are reacted at one time. Procedures of this type are commonly called "one-shot" reactions. U.S. Pat. No. 2,734,045 also addresses itself both to water-chain extended prepolymers and to "one-shot" polyurethane-ureas by mass polymerization techniques. U.S. Pat. No. 2,830,037 reveals the formation in organic solvents of prepolymeric chains extended with urea linkages via water at room temperature so as to provide small beads of polyurethane-ureas which are substantially cured. In U.S. Pat. No. 2,871,227 similarly is disclosed the preparation of a polyurethane-urea by initial preparation of a polyurethane-urea prepolymer or a one-shot mass polymerization of the starting material with subsequent cure of the rubbery mass thus attained.
All of the above techniques have suffered from numerous disadvantages. Aside from the expense of organic solvents, the formation of polyurethane-ureas in non-aqueous or in the presence of oranic solvent solutions has heretofore resulted in large particle size products due to the solvent swelling and tackiness-induced agglomeration of the product particles. In addition, it is readily apparent that solutions or aqueous dispersions of urethane-ureas are rather costly to ship should one desire to make solutions or dispersions at one location and subsequently use them at any place a substantial distance from the point of manufacture. Heretofore, the aqueous dispersions have been coagulated by special techniques to obtain solid urethane-ureas, as disclosed for example, in U.S. Pat. No. 3,402,149. However, it is advantageous to avoid the expense and inconvenience of these additional processing steps. Also, it is very difficult and time-consuming to filter the solids from the reaction medium and to control their particle sizes. Where the urethane-ureas have been formed as more or less unitary masses of substantial size, they may be readily shipped without undue expense, but if they are to be more advantageously used in large masses, such must be broken into small particles so as to facilitate further processing. Great difficulty is experienced in trying to reduce the tacky, rubbery particles to smaller sizes, especially since the urethane-ureas often have high tear strengths and hardness. It is, therefore, highly desirable to develop a process in which small particle form urethane-ureas are easily produced and separated in a "one-shot" process.